Slope tileh_north_aqueduct = GetTileSlope(tile_start);
			if (tileh_north_aqueduct != ComplementSlope(tileh_end)) {
				Slope tileh_north_result;
				switch (tileh_end) {
					case SLOPE_NE:
						switch (tileh_north_aqueduct) {
							case SLOPE_S:
							case SLOPE_STEEP_S:
								tileh_north_result = SLOPE_W;
								break;
							case SLOPE_W:
							case SLOPE_STEEP_W:
								tileh_north_result = SLOPE_S;
								break;
							default: NOT_REACHED();
						}
						break;

					case SLOPE_NW:
						switch (tileh_north_aqueduct) {
							case SLOPE_E:
							case SLOPE_STEEP_E:
								tileh_north_result = SLOPE_S;
								break;
							case SLOPE_S:
							case SLOPE_STEEP_S:
								tileh_north_result = SLOPE_E;
								break;
							default: NOT_REACHED();
					}
					break;

					case SLOPE_SW:
						switch (tileh_north_aqueduct) {
							case SLOPE_N:
							case SLOPE_STEEP_N:
								tileh_north_result = SLOPE_E;
								break;
							case SLOPE_E:
							case SLOPE_STEEP_E:
								tileh_north_result = SLOPE_N;
								break;
							default: NOT_REACHED();
						}
						break;

					case SLOPE_SE:
						switch (tileh_north_aqueduct) {
							case SLOPE_W:
							case SLOPE_STEEP_W:
								tileh_north_result = SLOPE_N;
								break;
							case SLOPE_N:
							case SLOPE_STEEP_N:
								tileh_north_result = SLOPE_W;
								break;
							default: NOT_REACHED();
						}
						break;

					default: NOT_REACHED();
				}