As mentioned in the text, the notation $\exists ! x P(x)$ denotes
"There exists a unique $x$ such that $P(x)$ is true."
If the domain consists of all integers, what are the truth values of these statements?
$$
\begin{array}{ll}{\text { a) } \exists ! x(x>1)} & {\text { b) } \exists ! x\left(x^{2}=1\right)} \\ {\text { c) } \quad \exists ! x(x+3=2 x)} & {\text { d) } \exists ! x(x=x+1)}\end{array}
$$