relational calculus

Question

Comments

quntifier is missing on a and b, assuming it to be $\exists$

answer should be 4

P	Q	U
2	b	5
2	b	6
2	c	5
3	d	6

 

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4 rows

T.P	T.Q	T.U
2	b	5
2	b	6
2	c	5
3	d	6

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If we don't use $\exists$ before a and b then they are free variable and the above theory can also be written as

{a.P, a.W, b.U / remaining query}

or

{a.P, b.Q, b.U / remaining query}

is it correct?