λ x : word64 * word64 * word64 * word64,
Interp-η
(λ var : Syntax.base_type → Type,
 λ '(x5, x6, x4, x2)%core,
 uint128_t x7 = (((uint128_t)x2 * x5) + (((uint128_t)x4 * x6) + (((uint128_t)x6 * x4) + ((uint128_t)x5 * x2))));
 uint128_t x8 = ((((uint128_t)x2 * x6) + ((0x2 * ((uint128_t)x4 * x4)) + ((uint128_t)x6 * x2))) + (0x1b * (0x2 * ((uint128_t)x5 * x5))));
 uint128_t x9 = ((((uint128_t)x2 * x4) + ((uint128_t)x4 * x2)) + (0x1b * (((uint128_t)x6 * x5) + ((uint128_t)x5 * x6))));
 uint128_t x10 = (((uint128_t)x2 * x2) + (0x1b * ((0x2 * ((uint128_t)x4 * x5)) + (((uint128_t)x6 * x6) + (0x2 * ((uint128_t)x5 * x4))))));
 uint128_t x11 = (x10 >> 0x3a);
 uint64_t x12 = ((uint64_t)x10 & 0x3ffffffffffffff);
 uint128_t x13 = (x11 + x9);
 uint128_t x14 = (x13 >> 0x39);
 uint64_t x15 = ((uint64_t)x13 & 0x1ffffffffffffff);
 uint128_t x16 = (x14 + x8);
 uint128_t x17 = (x16 >> 0x3a);
 uint64_t x18 = ((uint64_t)x16 & 0x3ffffffffffffff);
 uint128_t x19 = (x17 + x7);
 uint64_t x20 = (uint64_t) (x19 >> 0x39);
 uint64_t x21 = ((uint64_t)x19 & 0x1ffffffffffffff);
 uint128_t x22 = (x12 + ((uint128_t)0x1b * x20));
 uint64_t x23 = (uint64_t) (x22 >> 0x3a);
 uint64_t x24 = ((uint64_t)x22 & 0x3ffffffffffffff);
 uint64_t x25 = (x23 + x15);
 uint64_t x26 = (x25 >> 0x39);
 uint64_t x27 = (x25 & 0x1ffffffffffffff);
 return (Return x21, (x26 + x18), Return x27, Return x24))
x
     : word64 * word64 * word64 * word64 → ReturnType (uint64_t * uint64_t * uint64_t * uint64_t)