Elementary substructure
= Elementary substructure
{title2=$M\prec N$}
A substructure $M\subseteq N$ is elementary when every <first-order formula> with parameters from $M$ has the same truth value in $M$ and $N$.
= Elementary substructure
{title2=$M\prec N$}
A substructure $M\subseteq N$ is elementary when every <first-order formula> with parameters from $M$ has the same truth value in $M$ and $N$.