comments on gc struct and functions
projection function
Revert "comments on gc struct and functions"

This reverts commit eb35c49b2824d6009e7b8f5f3b79f588ee010a8e.
add factorial function.
call monadic user functions without quote!
	f<:y*2
	f3  =>  9
call dyadic user function without doublequote!
./inca
        f<:x+y
2:4
x+y
        2f3
0:
5
        f<4
0:
4
        2f3
0:
243