Classic Fourier Series

[Snorre]

Hi,

what the help doesn't mention is that zip doesn't work only on lists/vectors but also on a bivariate function and two scalars.
So, zip('+',2,3) gives 5.

unapply turns an expression into a function (see on-calc help):
unapply(expr,var1,...,varN) returns a function (var1,...,varN)->expr.

In fact the aim was something like "unapply(expr,var)", but not with "var" itself being the parameter but its value (another variable, e.g. "x").
That is "var:=x; unapply(expr,var)" will return "(var)->expr" -- not the desired "(x)->expr".
So, the zip construction evaluates "var" first before unapplying.