code: func uniqueMorphism() morphism {
  	return morphism{
  		Reversal: func(ctx *pathContext) (morphism, *pathContext) { return uniqueMorphism(), ctx },
  		Apply: func(in shape.Shape, ctx *pathContext) (shape.Shape, *pathContext) {
  			return shape.Unique{in}, ctx
  		},
  	}
  }
docs: // uniqueMorphism removes duplicate values from current path.