( ( If ( -LRB- ( resistivity ( -RRB- ( is ( equal ( to ( ( zero ( inside ( the superconductor ) ) ) ( while ( ( the current ) ( is flowing ) ) ) ) ) ) ) ) ) ) ) ( , ( ( the ( electric field ) ) ( ( must ( be zero ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (S (-LRB- -LRB-) (NP (NN resistivity)) (-RRB- -RRB-) (VP (VBZ is) (ADJP (JJ equal) (S (VP (TO to) (VP (VB zero) (PP (IN inside) (NP (DT the) (NN superconductor))) (SBAR (IN while) (S (NP (DT the) (NN current)) (VP (VBZ is) (VP (VBG flowing)))))))))))) (, ,) (NP (DT the) (JJ electric) (NN field)) (VP (MD must) (VP (VB be) (NP (CD zero)))) (. .)))
If (resistivity) is equal to zero inside the superconductor while the current is flowing, the electric field must be zero.
(ROOT (S (NP (NNS Superconductors)) (VP (VBP are) (NP (NP (NNS materials)) (PP (IN with) (NP (NP (DT a) (NN resistivity)) (PP (IN of) (NP (CD zero))))))) (. .)))