subf — symbolic subtraction
["c"]=subf("a","b")
strings
returns the character string c="a-b" Trivial simplifications such as subf("0","a") or subf("1","2") are performed.
c
"a-b"
subf("0","a")
subf("1","2")
subf('0','a') subf('2','1') subf('a','0')