fn sum(env: soroban_sdk::Env, operand1: i32, operand2: i32) -> i32
fn sub(env: soroban_sdk::Env, operand1: i32, operand2: i32) -> i32
fn mul(env: soroban_sdk::Env, operand1: i32, operand2: i32) -> i32
fn div(env: soroban_sdk::Env, operand1: i32, operand2: i32) -> Option
fn all_op(env: soroban_sdk::Env) -> soroban_sdk::Vec
fn get_op(env: soroban_sdk::Env, index: u32) -> Option
fn last_op(env: soroban_sdk::Env) -> Option