question: public final int first_common_layer ( BrdItem p_other ) { int max_first_layer = Math . max ( first_layer ( ) , p_other . first_layer ( ) ) ; int min_last_layer = Math . min ( last_layer ( ) , p_other . last_layer ( ) ) ; if ( max_first_layer > min_last_layer ) { return - 1 ; } return max_first_layer ; }
target:  Returns the first layer, where both this item and p_other have a shape.  Returns -1, if such a layer does not exisr.