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{SECT 0 {PARA 0 "" 0 "" {TEXT -1 0 "" }}{SECT 0 {PARA 0 "" 0 "" {TEXT 
26 8 "Advice: " }{TEXT -1 30 "Changing assumptions and names" }}{PARA 
0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 186 "Strange things
 happen to an expression containing a variable on which assumptions ha
ve been made, when those assumptions are changed or a value is assigne
d to the variable.  For example:" }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 
1 0 14 "assume(x > 0);" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 8 "a:
= x+1:" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 20 "additionally(x < \+
2);" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 4 "a-x;" }}{PARA 11 "" 
1 "" {XPPMATH 20 "6#,(%#x|irG\"\"\"F%F%%#x|irG!\"\"" }}}{PARA 0 "" 0 "
" {TEXT -1 243 "This effect is due to the fact that when an assumption
 is made about a variable, the name of that variable is changed.  If t
he \"Trailing Tildes\" option for assumed variables is being used (whi
ch is the default), the new name is printed with a " }{MPLTEXT 0 21 1 
"~" }{TEXT -1 232 ".  The name change occurs even without this option \+
(the option has only a cosmetic effect, changing how the name is print
ed) .  This is an illustration of the fact that two names that look th
e same to us can be different to Maple.  " }}{EXCHG {PARA 0 "> " 0 "" 
{MPLTEXT 1 0 18 "assume(x,integer);" }}}{EXCHG {PARA 0 "> " 0 "" 
{MPLTEXT 1 0 2 "x;" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#%#x|irG" }}}
{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 9 "about(x);" }}{PARA 6 "" 1 "" 
{TEXT -1 25 "Originally x, renamed x~:" }}{PARA 6 "" 1 "" {TEXT -1 27 
"  is assumed to be: integer" }}{PARA 6 "" 1 "" {TEXT -1 0 "" }}}
{PARA 0 "" 0 "" {TEXT -1 86 "The old name is assigned the new name as \+
its value.  Thus when you enter and evaluate " }{MPLTEXT 0 21 1 "x" }
{TEXT -1 29 ",  you obtain the new name.  " }}{EXCHG {PARA 0 "> " 0 "
" {MPLTEXT 1 0 6 "'x'-x;" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#,&%\"xG\"
\"\"%#x|irG!\"\"" }}}{PARA 0 "" 0 "" {TEXT -1 40 "Here we delayed eval
uation of the first " }{MPLTEXT 0 21 1 "x" }{TEXT -1 46 " by putting i
t in forward quotes.  The second " }{MPLTEXT 0 21 1 "x" }{TEXT -1 183 
" was evaluated normally.  The result is the difference of two distinc
t variables, instead of 0.  If evaluation is allowed to occur (e.g. by
 recalling the last result), we do get 0.   " }}{EXCHG {PARA 0 "> " 0 
"" {MPLTEXT 1 0 2 "%;" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#\"\"!" }}}
{PARA 0 "" 0 "" {TEXT -1 121 "The new name can't be entered directly f
rom the keyboard: it is not the same as what you get by entering the s
tring `x~`." }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 7 "`x~`-x;" }}
{PARA 11 "" 1 "" {XPPMATH 20 "6#,&%#x|irG\"\"\"%#x|irG!\"\"" }}}{PARA 
0 "" 0 "" {TEXT -1 38 "Now if a new assumption is made about " }
{MPLTEXT 0 21 1 "x" }{TEXT -1 7 " using " }{MPLTEXT 0 21 6 "assume" }
{TEXT -1 4 " or " }{MPLTEXT 0 21 12 "additionally" }{TEXT -1 26 ", we \+
get another new name " }{MPLTEXT 0 21 2 "x~" }{TEXT -1 56 " that is di
fferent from the previous one.  The original " }{MPLTEXT 0 21 1 "x" }
{TEXT -1 80 " is assigned this as a value, so when any expression that
 contains the original " }{MPLTEXT 0 21 1 "x" }{TEXT -1 22 " is evalua
ted the new " }{MPLTEXT 0 21 2 "x~" }{TEXT -1 33 " will be used.  But \+
the previous " }{MPLTEXT 0 21 2 "x~" }{TEXT -1 94 " is left unchanged,
 so that evaluation of an expression that contains it will not use the
 new " }{MPLTEXT 0 21 2 "x~" }{TEXT -1 28 ".  Similarly, if you assign
 " }{MPLTEXT 0 21 1 "x" }{TEXT -1 56 " a value you are not affecting e
xpressions that contain " }{MPLTEXT 0 21 2 "x~" }{TEXT -1 1 "." }}
{PARA 0 "" 0 "" {TEXT -1 0 "" }}{PARA 0 "" 0 "" {TEXT -1 47 "A cure fo
r these problems is to assign the new " }{MPLTEXT 0 21 2 "x~" }{TEXT 
-1 29 " or the new value to the old " }{MPLTEXT 0 21 2 "x~" }{TEXT -1 
15 " as well as to " }{MPLTEXT 0 21 1 "x" }{TEXT -1 74 ".  It can be d
one as follows.  Note that we must save the name of the old " }
{MPLTEXT 0 21 2 "x~" }{TEXT -1 60 " in a variable before changing the \+
assumption.  We then use " }{MPLTEXT 0 21 6 "assign" }{TEXT -1 13 " ra
ther than " }{MPLTEXT 0 21 2 ":=" }{TEXT -1 55 " because we want to ma
ke an assignment to the value of " }{MPLTEXT 0 21 4 "oldx" }{TEXT -1 
31 " (which is the name of the old " }{MPLTEXT 0 21 2 "x~" }{TEXT -1 
17 ") rather than to " }{MPLTEXT 0 21 4 "oldx" }{TEXT -1 8 " itself." 
}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 24 "assume(x > 0);\na:= x+1:\n
" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 47 "oldx:= x:\nadditionally
(x < 2);\nassign(oldx,x):\n" }}}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 
4 "a-x;" }}{PARA 11 "" 1 "" {XPPMATH 20 "6#\"\"\"" }}}{PARA 0 "" 0 "" 
{TEXT -1 41 "Similarly, this technique will work when " }{MPLTEXT 0 
21 1 "x" }{TEXT -1 99 " is being assigned a value.  But the simplest t
hing to do in that case is to assign the value with " }{MPLTEXT 0 21 
6 "assign" }{TEXT -1 13 " rather than " }{MPLTEXT 0 21 2 ":=" }{TEXT 
-1 1 "." }}{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 12 "assign(x,2);" }}}
{EXCHG {PARA 0 "> " 0 "" {MPLTEXT 1 0 2 "a;" }}{PARA 11 "" 1 "" 
{XPPMATH 20 "6#\"\"$" }}}}{SECT 0 {PARA 0 "" 0 "" {TEXT 26 9 "See also
:" }{TEXT -1 1 " " }{HYPERLNK 17 "about" 2 "about" "" }{TEXT -1 2 ", \+
" }{HYPERLNK 17 "assign" 2 "assign" "" }{TEXT -1 2 ", " }{HYPERLNK 17 
"assume" 2 "assume" "" }{TEXT -1 2 ", " }{HYPERLNK 17 "Error: cannot a
ssume on a constant object" 2 "Error:cannot_assume_on_a_constant_objec
t" "" }{TEXT -1 2 ", " }{HYPERLNK 17 "Obtaining properties of objects
" 2 "Obtaining_properties_of_objects" "" }}}{SECT 0 {PARA 0 "" 0 "" 
{TEXT 26 24 "Maple Advisor Database, " }{TEXT -1 15 " R. Israel 1997" 
}}}}{MARK "2 0 0" 4 }{VIEWOPTS 1 1 0 1 1 1803 1 1 1 1 }{PAGENUMBERS 0 
1 2 33 1 1 }