Do you know what functions KGETBL, KGETIN, MADIN, and MADOUT do? Also, do you know what the format DATFOR does? The format is "14A6 *" which I would guess reads 14 cards with 6 alphabetic characters each? Maybe LETTER converts the input characters to tokens of the IDENT format. Everything I look at leads to another mystery :-)

It looks like IS is the parenthesization level, IC counts the character within a card (1 to 6) and IW counts selects the card (1-14).