Quickest way to check if a number is in a set?

 all(m1[,1]==m1)
 # [1] TRUE
 all(m2[,1]==m2)
 #[1] FALSE

 m1 <- matrix(c(10:1, 10:1, 10:1), ncol=3)
 m2 <- cbind(m1, 11:2)

boolean function isPrime(num)

  //1, 0 and negatives cannot be prime.
  if (num < 2) then
    return false
  endif

  // 2 is the only even prime.
  if (num MOD 2 = 0) then
    return (num = 2)
  endif

  // Check for odd factors.
  limit <- sqrt(num)
  for (factor <- 3; factor <= limit; factor <- factor + 2) do
    if (num MOD factor = 0) then
      return false
    endif
  endfor

  // If we reach this point then the number is prime.
  return true

endfunction