EOL
do {
    if (At_BOL) {
	Ins_Char('1')		// add new digit
	Break
    }
    Char(-1)
    #1 = Cur_Char+1		// digit
    #2 = 0			// carry bit
    if (#1 > '9') {
	#1 = '0'
	#2 = 1
    }
    Ins_Char(#1, OVERWRITE)
    Char(-1)
} while (#2)			// repeat until no carry