Determine if a grid contains another grid
Brachylog (v2), 4 bytes

s\s\


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Most easily run as a full program, as usual for a decision-problem, with a specified as a command-line argument, b on standard input. The question asks for a function, and the program also works as a function, with b on the left, a on the right, and output via producing an exception if and only if the decision is  false.

Explanation

s\s\
s     a substring of rows of {the left input}
 \…\  assert rectangular; swap row and column operations
  s   a substring of &lt;s&gt;rows&lt;/s&gt; columns of {the above matrix}
      {implicit} assert that the result can be {the right input}


The "assert rectangular" is, obviously, pointless, as the question guarantees that already. The rest of the program does the grid-finding for us by identifying a substring of the rows and of the columns, i.e. a submatrix.

Meta-discussion

We've had a very similar question before; I'd expect most answers to one question to be modifiable into answers to the other. I think this is the neater version of it, though.