ERC-4337 (account abstraction)

Code running on a blockchain (Solidity, Rust) that auto-executes an agreement. A single bug can cost nine figures · why we audit, fuzz, and threat-model before deploy.

The primary language for EVM-compatible blockchains (Ethereum, Arbitrum, Base). Pascal-like syntax, low-level memory handling, TS-compatible toolchain (Foundry, Hardhat).

The shared execution environment across Ethereum and compatible chains (Arbitrum, Base, Polygon, Optimism). Writing a contract here means it runs on all of them.

A secondary network (Arbitrum, Base, Optimism, zkSync) settling on Ethereum (L1) but much faster and cheaper. Rollups bring 10-100× lower gas.

A test that verifies a universal rule ('sum of user balances always equals total supply'). Feeds the contract random transaction sequences; the rule must hold in every state.

Running millions of pseudo-random inputs through a function to find a combination that breaks it. Echidna or Foundry fuzz campaigns.