code: func isPubkey(pops []parsedOpcode) bool {
  	// Valid pubkeys are either 33 or 65 bytes.
  	return len(pops) == 2 &&
  		(len(pops[0].data) == 33 || len(pops[0].data) == 65) &&
  		pops[1].opcode.value == OP_CHECKSIG
  }
docs: // isPubkey returns true if the script passed is a pay-to-pubkey transaction,
  // false otherwise.