Invention of the telephone useful and widespread apparatus it is now. The telephone exchange was an idea of the Hungarian engineer Tivadar Puskás (1844–1893) in 1876, while he was working for Thomas Edison on a telegraph exchange. Puskás was working on his idea for an electrical telegraph exchange when Alexander Graham Bell received the first patent for the telephone. This caused Puskás to take a fresh look at his own work and he refocused on perfecting a design for a telephone exchange. He then got in touch with the U.S. inventor Thomas Edison who liked the design. According to Edison, "Tivadar Puskas was the
Disclosure of the invention under the European Patent Convention patent application as filed, consisting in an insufficient identification of the subject-matter claimed, cannot subsequently be cured without offending against Article 123(2) EPC which provides that the subject-matter content of a European patent application as filed may not be extended. An insufficiently clear and complete disclosure of the invention is a ground of opposition, and revocation. Although the European Patent Convention does not exclude the patenting of "revolutionary" inventions,<ref name="T 1329/07"> Decision T 1329/07 of the Technical Board of Appeal 3.4.02 of 11 November 2010, point 2.2.3</ref> The burden of proof generally lies upon an opponent to establish insufficiency of