a < b {\displaystyle a<b} (10) [前提] c < d {\displaystyle c<d} (15) [前提] a − b < 0 {\displaystyle a-b<0} (20) 源自 (10) 0 < d − c {\displaystyle 0<d-c} (25) 源自 (15)
a − b < d − c {\displaystyle a-b<d-c} (30) 源自 (20) (25) a − b + ( b + c ) < d − c + ( b + c ) {\displaystyle a-b+(b+c)<d-c+(b+c)} (35) 源自 (30) a + c < b + d {\displaystyle a+c<b+d} (40) 源自 (35) [結論]
