The types of chemical changes that are discussed here include combination and decomposition. Combination happens when two or more substances combine together in a chemical reaction to form one or more different substances. Combination reactions can result in the corrosion of metals like iron with oxygen from the air. Combustion reactions, such as a burning candle, are also examples of the chemical change through the combination of wax and oxygen in a reaction that produces heat, light, carbon dioxide and water.
When running iOS 7 or iOS 8, all iPhone models use Helvetica Ultra Light or Helvetica Light. Finally, when running iOS 9, all iPhone models use a font that is fairly similar to Helvetica, but that Apple calls San Francisco and that is shared by the Apple Watch. iPod models released prior to the iPhone use either Chicago, Espy Sans, or Myriad and use Helvetica after the release of the iPhone.
So on an iPhone keyboard, easiest way I found; 1. Go into settings>general>keyboards. 2. Click on select new keyboard, then pick a Greek keyboard. Then when you go to type out your text, do it as normal, but then when you need to pi symbol, press the little round globe symbol next to the 123 on the keyboard. You will see the pi symbol on your Greek keyboard. Use it from there and then just go back and continue the rest in English.