  The aim of this paper is to prove energy conservation for the incompressible
Euler equations in a domain with boundary. We work in the domain
$\mathbb{T}^2\times\mathbb{R}_+$, where the boundary is both flat and has
finite measure.
  However, first we study the equations on domains without boundary (the whole
space $\mathbb{R}^3$, the torus $\mathbb{T}^3$, and the hybrid space
$\mathbb{T}^2\times\mathbb{R}$). We make use of some of the arguments of Duchon
\& Robert ({\it Nonlinearity} {\bf 13} (2000) 249--255) to prove energy
conservation under the assumption that $u\in L^3(0,T;L^3(\mathbb{R}^3))$ and
one of the two integral conditions \begin{equation*} \lim_{|y|\to
0}\frac{1}{|y|}\int^T_0\int_{\mathbb{R}^3} |u(x+y)-u(x)|^3\,d x\,d t=0
\end{equation*} or \begin{equation*}
  \int_0^T\int_{\mathbb{R}^3}\int_{\mathbb{R}^3}\frac{|u(x)-u(y)|^3}{|x-y|^{4+\delta}}\,d
x\,d y<\infty,\qquad\delta>0, \end{equation*} the second of which is equivalent
to requiring $u\in L^3(0,T;W^{\alpha,3}(\mathbb{R}^3))$ for some $\alpha>1/3$.
  We then use the first of these two conditions to prove energy conservation
for a weak solution $u$ on $D_+:=\mathbb{T}^2\times \mathbb{R}_+$: we extend
$u$ a solution defined on the whole of $\mathbb{T}^2\times\mathbb{R}$ and then
use the condition on this domain to prove energy conservation for a weak
solution $u\in L^3(0,T;L^3(D_+))$ that satisfies \begin{equation*} \lim_{|y|\to
0}
\frac{1}{|y|}\int^{T}_{0}\iint_{\mathbb{T}^2}\int^\infty_{|y|}|u(t,x+y)-u(t,x)|^3
\,d x_3 \,d x_1 \,d x_2 \,d t=0, \end{equation*} and certain continuity
conditions near the boundary $\partial D_+=\{x_3=0\}$.
