飞鸟鱼虫菲菲
Proof questions, proof (process) and formula derivation in mathematics are respectively in English数学公式是人们在研究自然界物与物之间时发现的一些联系，并通过一定的方式表达出来的一种表达方法，能够表征自然界不同事物之数量之间的或等或不等的联系。 它确切的反映了事物内部和外部的关系，是人们从一种事物到达另一种事物的依据，并且使人们更好的理解事物的本质和内涵。根据谓词逻辑的语义推导规则，语义应该具有一致性，就是对于一个命题逻辑语句集f，当且仅当至少存在这样一种解释i，f的一切元素在i之下都是真的，那么，f是语义一致的 。在命题逻辑语义学内，一个赋值不能同时把真和假给予某个命题原子式。在命题逻辑语义学中，在同一解释下，一个集合不能既属于某个谓词的外延又不属于该谓词的外延。
刘小淼淼淼
(a) if A=C and B=D, of course AxB=CxD.if AxB=CxD and A,B,C,D non-empty. If A is not equal to C, let's say A has an element a that does not belong to C. Since B and D are non-empty, there must be a pair with element a in AxC, but that pair does not belong to CxD since element a does not belong to C in the first place. So A must be equal to C. Likewise B must be equal to D.(b) if A=C and B=D, then AxB=CxD.(c) if A is empty, AxB is empty, if C is empty, CxD is also empty. So B can differ from D, but AxB still equals CxD.
优质英语培训问答知识库
