解 在$\triangle ADB$和$\triangle BCA$中,
$\{\begin {array}{l}\ \mathrm {A}D = BC,\\BD = AC,\\AB = BA,\end {array}.$
$∴\triangle ADB\cong \triangle BCA(\mathrm {SSS})$.
$∴∠ABD = ∠CAB$,$∠DAB = ∠CBA$,$∠D = ∠C$.
$∴∠DAB - ∠CAB = ∠CBA - ∠ABD$,
即$∠DAE = ∠CBE$.
在$\triangle DAE$和$\triangle CBE$中,
$\{\begin {array}{l} ∠D = ∠C,\\AD = BC,\\∠DAE = ∠CBE,\end {array}.$
$∴\triangle DAE\cong \triangle CBE(\mathrm {ASA})$.
$∴DE = CE$.