This procedure takes as input an expression and a list of variables and returns 1 if there are multiple occurrences of at least one variable. For example
MultipleOccurence(x^2+y^2-1,[x,y])will return 0 while
MultipleOccurence(x^2+x+y^2-1,[x,y]);will return 1.
This procedure is useful to test the transformation of an expression: is there is no multiple occurrences of variables in an expression, then the interval evaluation of this expression will be exact in the sense that it will return the exact lower and upper bounds of the expression for given intervals for the variables (which is not the case when multiple occurrence of variables appear in an expression).