Add formula generation for equ,neq,geq,leq,dgs and a command suggestion

[loader3229]

Add formula generation for equ,neq,geq,leq,dgs
equ $0,$1 -> ($0 == $1)
neq $0,$1 -> ($0 != $1)
geq $0,$1 -> ($0 >= $1)
leq $0,$1 -> ($0 <= $1)
dgs $0,$1 -> sumdigits($0,$1) for positive $0
dgs $0,$1 -> sumdigits($0,$1)*sign($0) for all $0
Also, a command suggestion: cmp $0,$1: compare $0,$1, if $0>$1 set $0 to 1;if $0<$1 set $0 to -1;if $0 equals $1 set $0 to 0; formula: sign($0-$1)
per $0,$1: compute Permutation coefficient (choose $1 items in $0 different items, different permutations): $0 := ($0-0)($0-1)($0-2)($0-3)...($0-$1+1), if $1 is 0 set $0 to 1, if $1 is negative set $0 to 0. formula for non-negative $0 and $0-$1: floor($0!/($0-$1)!)
These formulas are compatible with the PARI/GP syntax.