@article{Hopcroft:1969,
    Abstract = {LetG andG 0 be context-free grammars. Necessary and sufficient conditions onG 0 are obtained for the decidability ofL(G 0) \$\$ {\backslash}subseteq \$\$ L((G) It is also shown that it is undecidable for whichG 0,L(G) \$\$ {\backslash}subseteq \$\$ is decidable. Furthermore, given thatL(G) \$\$ {\backslash}subseteq \$\$ is decidable for a fixedG 0, there is no effective procedure to determine the algorithm which decidesL(G) \$\$ {\backslash}subseteq \$\$ IfL(G 0) is a regular set,L(G) = L(G 0) is decidable if and only ifL(G 0) is bounded. However, there exist non-regular, unboundedL(G 0) for whichL(G) = L(G 0) is decidable.},
    Author = {Hopcroft, J. E.},
    File = {On the equivalence and containment problems for context-free languages - Hopcroft (0) (0) - a - a - t.pdf},
    ISSN = {1433-0490},
    Journal = {Mathematical systems theory},
    Number = {2},
    Pages = {119--124},
    Title = {On the equivalence and containment problems for context-free languages},
    URL = {http://dx.doi.org/10.1007/BF01746517},
    Volume = {3},
    Year = {1969},
    bdsk-url-1 = {http://dx.doi.org/10.1007/BF01746517},
    date-added = {2016-01-13 12:21:45 +0000},
    date-modified = {2016-01-13 12:22:06 +0000},
    doi = {10.1007/BF01746517}
}

@article{Hopcroft:1969, Abstract = {LetG andG 0 be context-free grammars. Necessary and sufficient conditions onG 0 are obtained for the decidability ofL(G 0) \$\$ {\backslash}subseteq \$\$ L((G) It is also shown that it is undecidable for whichG 0,L(G) \$\$ {\backslash}subseteq \$\$ is decidable. Furthermore, given thatL(G) \$\$ {\backslash}subseteq \$\$ is decidable for a fixedG 0, there is no effective procedure to determine the algorithm which decidesL(G) \$\$ {\backslash}subseteq \$\$ IfL(G 0) is a regular set,L(G) = L(G 0) is decidable if and only ifL(G 0) is bounded. However, there exist non-regular, unboundedL(G 0) for whichL(G) = L(G 0) is decidable.}, Author = {Hopcroft, J. E.}, File = {On the equivalence and containment problems for context-free languages - Hopcroft (0) (0) - a - a - t.pdf}, ISSN = {1433-0490}, Journal = {Mathematical systems theory}, Number = {2}, Pages = {119--124}, Title = {On the equivalence and containment problems for context-free languages}, URL = {http://dx.doi.org/10.1007/BF01746517}, Volume = {3}, Year = {1969}, bdsk-url-1 = {http://dx.doi.org/10.1007/BF01746517}, date-added = {2016-01-13 12:21:45 +0000}, date-modified = {2016-01-13 12:22:06 +0000}, doi = {10.1007/BF01746517} }