predsxxminusx0xminusxsypredminusxyquot0sy0quotsxsysquotminusxysyminusxsypredminusxyminusxsyminusxyquotsxsyquotminusxysyquotsxsyminusxytruequotsxsyquotminusxysytrue1231quot211s1111minus211pred111000quot2111quotsxsyminusxyfalse12minusxsyminusxytrue1minus22minusxsypredminusxyfalse