Published online by Cambridge University Press: 20 November 2018
We give necessary and sufficient conditions of the   ${{L}^{p}}$ -well-posedness (resp.
 ${{L}^{p}}$ -well-posedness (resp.   $B_{p,\,q}^{s}$ -wellposedness) for the second order degenerate differential equation with finite delays
 $B_{p,\,q}^{s}$ -wellposedness) for the second order degenerate differential equation with finite delays
  $${{\left( Mu \right)}^{\prime \prime }}\left( t \right)+B{u}'\left( t \right)+Au\left( t \right)=G{{{u}'}_{t}}+F{{u}_{t}}+f\left( t \right),\left( t\in \left[ 0,2\pi\right] \right)$$
 $${{\left( Mu \right)}^{\prime \prime }}\left( t \right)+B{u}'\left( t \right)+Au\left( t \right)=G{{{u}'}_{t}}+F{{u}_{t}}+f\left( t \right),\left( t\in \left[ 0,2\pi\right] \right)$$
with periodic boundary conditions   $\left( Mu \right)\,\left( 0 \right)\,=\,\left( Mu \right)\,\left( 2\pi\right),\,{{\left( Mu \right)}^{\prime }}\left( 0 \right)\,=\,{{\left( Mu \right)}^{\prime }}\left( 2\pi\right)$ , where
 $\left( Mu \right)\,\left( 0 \right)\,=\,\left( Mu \right)\,\left( 2\pi\right),\,{{\left( Mu \right)}^{\prime }}\left( 0 \right)\,=\,{{\left( Mu \right)}^{\prime }}\left( 2\pi\right)$ , where   $A,\,B,\,\text{and}\,M$  are closed linear operators on a complex Banach space
 $A,\,B,\,\text{and}\,M$  are closed linear operators on a complex Banach space   $X$  satisfying
 $X$  satisfying   $D\left( A \right)\,\cap \,D\left( B \right)\,\subset \,D\left( M \right)$ ,
 $D\left( A \right)\,\cap \,D\left( B \right)\,\subset \,D\left( M \right)$ ,   $F\,\text{and}\,G$  are bounded linear operators from
 $F\,\text{and}\,G$  are bounded linear operators from   ${{L}^{p}}\left( \left[ -2\pi ,\,0 \right];\,X \right)\,\left( \text{resp}\text{.}\,\text{B}_{p,q}^{s}\left( \left[ -2\pi ,\,0 \right];\,X \right) \right)$  into
 ${{L}^{p}}\left( \left[ -2\pi ,\,0 \right];\,X \right)\,\left( \text{resp}\text{.}\,\text{B}_{p,q}^{s}\left( \left[ -2\pi ,\,0 \right];\,X \right) \right)$  into   $X$ .
 $X$ .