I have an idea for terraforming both Mars AND Venus. Or atleast transform the atmospheres to be survivable for human using only respirator, without need for pressurized suit.

Premesis:

1. Venus has too much gas (CO2). Too high pressure and greenhouse effect.
2. Mars has too little gas. Too low atmosperic pressure, ang greenhouse effect.
3. There is 90× as much gas in Venus that is needed in Mars. Altough maybe only just enough nitrogen for one planet for earth like atmosphere.
4. Venus is closer to the sun, while Mars is furher away.
5. Solar sail can be used to propel stuff away from the sun.

tecnological requirements:

1. Space elevator; (perhaps with graphene cables)
2. orbital manufacturing, using mainly CO2, sulphuric acid and sunlight;
3. functional solar sail (not absolutely nesessary as Venus has enough excess gas to be used as propellant).

Steps to carry out the step 1. Build a space elevator in Venus.

step 2. Build a manufactacturing facility on top of the space elevator that runs with material sourced from the atmophere of Venus, and solar energy.

step 2.5. Use the facility to build more space elevators and orbital manufacturing facilities.

step 3. Build a massive fleet of solar sail freighters that will carry needed amounth of Venus atmosphere to Mars in solid state.

step 4. Pump atmosphere to pressurized shaded containers in the orbit, for cooling below freezing tempersture.

step 5. Send packaged athmospere towards Venus on Solar sail freighters. Part of the cargo can be used as propellant if needed, or if solar sail isn't feasible.

step 5. Reusing the freighters The freighters could be reusable by using combination of gravitational slingshot around Mars and ejection of the cargo at high velocity to gain needed thrust to get back to Venus (slow orbital speed around sun). Don't know if solar sail could be used to actually "sail" croswind, as to slow down the orbital speed around the sun. If it works, then the sail could be used to manouver the return flight. If not, it would be retracted and only deployed to adjust speed to regain orbit with Venus.

step. 6 repeat untill Mars has enough atmosphic pressure and greenhouse gasses.

step 7. perhaps create a small organic moon of the rest of the excess gas around Venus and mars for later use and topping up the atmosphere when needed.

An other idea to trap CO2 from atmosphere of Venus:

We could create billions of tons of artificial diamonds out of the atmospheric CO2 on Venus. Diamonds would not corrode from sulphuric acid rain that Venus currently experiences. Later there might be ways to trap CO2 with syntethic photosyntesis to decrease atmospheric pressure.