Reflection of the bright sky in the smooth surface of the night riverReflection of the bright sky in the smooth surface of the night river
The rays of the setting sun gliding across the water surfaceThe rays of the setting sun gliding across the water surface
Where is the water surface, and where is the sky, everything has mergedWhere is the water surface, and where is the sky, everything has merged
В математике: граница, отделяющая геометрическое тело от внешнего пространства. Наружная сторона чего-н..