https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=56270
/** A single expression of type B, K, or V. Specifically, this can't be an
     * and_v or an expression of type W (a: and s: wrappers). */
    SINGLE_BKV_EXPR,
    /** Potentially multiple SINGLE_BKV_EXPRs as children of (potentially multiple)
     * and_v expressions. Syntactic sugar for MAYBE_AND_V + SINGLE_BKV_EXPR. */
    BKV_EXPR,
    
    W_EXPR,
    /** SWAP expects the next element to be OP_SWAP (inside a W-type expression that
     * didn't end with FROMALTSTACK), and wraps the top of the constructed stack
     * with s: */
    SWAP,
    /** ALT expects the next element to be TOALTSTACK (we must have already read a
     * FROMALTSTACK earlier), and wraps the top of the constructed stack with a: */
    ALT,
    
    CHECK,
    
    DUP_IF,
    
    VERIFY,
    
    NON_ZERO,