letrec1.lean:6:0-9:7: error: 'f1.g' has already been declared
letrec1.lean:18:35-18:36: error: unknown identifier 'g'
letrec1.lean:27:8-28:9: error: invalid type in 'let rec', it uses 'f' which is being defined simultaneously
letrec1.lean:37:10-37:50: error: invalid type in 'let rec', it uses 'g' which is being defined simultaneously