subs() performs "syntactic substitution" as in Maple; you can substitute

subs() performs "syntactic substitution" as in Maple; you can substitute
any object by any other object (even numerics) but only when the object
subs() is called on exactly matches an object on the left-hand side of the
substitution list; expairseq still doesn't substitute its numeric coefficients
so substituting numerics will not replace them in all occurences (this
shouldn't matter, though)