why doesn't it work

tieneAncestro: unmamif
    dad isNil & mom isNil
        ifTrue: [ ^ false ]
        ifFalse:[
                ((unmamif == dad) | (unmamif == mom))
                    ifTrue: [ ^ true ]
                    ifFalse: [
                        mom isNil
                            ifFalse: [ (mom tieneAncestro: unmamif) ifTrue: [ ^ true ]. ].
                        dad isNil
                            ifFalse: [ (dad tieneAncestro: unmamif) ifTrue: [ ^ true ]. ]
                                ].
                    ].