/* Return 1 if two yx_uint16 coordinates at "a" and "b" are equal, else 0. */
extern uint8_t yx_uint16_cmp(struct yx_uint16 * a, struct yx_uint16 * b);
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/* Return yx_uint16 coordinate one step from coordinate yx in direction "dir"
* (east: 'E', west: 'W', north: 'N', south: 'S').
*