Denote G ( s ) = ∫ ∫ 0 s g ( t ) d t . Let u ∈ ∈ L l o c ∞ ∞ ( R n ) , ∇ ∇ u ∈ ∈ L 2 ( R n ) , G ( u ( ⋅ ⋅ ) ) ∈ ∈ L 1 ( R n ) , n ∈ ∈ N , be a solution to the equation − − ∇ ∇ 2 u = g ( u ) , in the sense of distributions. Then u satisfies the relation ( n − − 2 2 ) ∫ ∫ R n | ∇ ∇ u ( x ) | 2 d x = n ∫ ∫ R n G ( u ( x ) ) d x .