Press xfM again:

(+ 4 (+ 3 (+ 2 ( cond ((<= 1 0) 0) ((= 1 1) 1) ((> 1 1) (+ 1 (triangle-using-cond (1- 1))))))))

Evaluate the cond branches in your mind and simplify with akrr .

(+ 4 (+ 3 (+ 2 1 )))