pub fn is_send(&self) -> bool {
        F::ORDER_U32.div_ceil(2) <= self.0[6].as_canonical_u32() &&
            self.0[6].as_canonical_u32() <= (F::ORDER_U32 - 1)
    }
Returns whether the extension field element viewed as an y-coordinate of a digest represents
a send interaction.
crates/stark/src/septic_extension.rs