Error, (in ...) cannot determine if this expression is true or false: ...
Maple cannot determine whether something is true or false in an if statement or while clause.
A typical occurrence happens when a procedure that requires numeric arguments is called with symbolic arguments:
f:=procxifx<0thenx^3elsex^2end ifend proc
Error, (in f) cannot determine if this expression is true or false: x < 0
Maple evaluates the inputs to a procedure such as plot before it calls the procedure, resulting in f being called with the symbolic argument x. Since x has not yet been assigned a value, Maple cannot determine if x is less than 0. You can either delay the evaluation of the input using unevaluation quotes, or you can supply the arguments with operator form. For details, see uneval.
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