class Human<Sex, ComplementarySex> { ComplementarySex spouse; void marryTo(ComplementarySex spouse) { this.spouse = spouse; } } class Man extends Human<Man, Woman> {} class Woman extends Human<Woman, Man> {} なんだ，結局一緒じゃないか． class MSM extends Human<MSM, MSM> {} class WSW extends Human<WSW, WSW></wsw,></msm,></woman,></man,></sex,>…